1. Field of the Invention
The present invention relates to an image reading apparatus such as a scanner which reads an image on an original conveyed using a conveying mechanism such as a roller, and a control method of the image reading apparatus.
2. Description of the Related Art
An example of a conventional image reading apparatus is shown in FIG. 30.
The image reading apparatus shown in FIG. 30 includes a lower unit 301 and an upper unit 302 supported so as to be vertically turnable via a hinge 313 with respect to the lower unit 301. A turning movement of the upper unit 302 causes an original conveying section to open and/or close. An opened state and/or a closed state of the original conveying section is detected by an opening-closing detection sensor 337. A convey path is formed when the original conveying section assumes a closed state to enable conveying of an original.
The image reading apparatus starts an image reading operation based on a control signal from a manual operation section, not shown, or from the outside of the image reading apparatus. First, an original mounting table 307 is elevated until an uppermost original 308 of a stack of originals placed on the original mounting table 307 abuts a pickup roller 306. After the original mounting table 307 is sufficiently elevated, the original 308 is fed to the convey path by the pickup roller 306 and a feeding roller 304 that is a feed unit.
When two or more originals 308 are picked up by the pickup roller 306 at the same time, the originals are separated by a retard roller 311 and fed to the convey path one by one. Images on each of originals 308 sent to the convey path to be separated and fed are read by an image sensor 312 on the convey path, and image data is transferred to an image processing section, not shown. The front end and the rear end of an original 308 conveyed along the convey path are detected by a registration sensor 314. Conveying timing and the like are controlled by signals from the registration sensor 314.
A platen roller 310 is disposed at a position opposing the image sensor 312 across the convey path of the original 308. The platen roller 310 is used as a background member that causes the background color of an image of the original 308 read by the image sensor 312 to be changeable. A predetermined clearance gap is provided between the platen roller 310 and the image sensor 312.
More specifically, the platen roller 310 is arranged so that, for example, an approximately half of the outer peripheral surface thereof is a black portion and the remaining approximately half of the outer peripheral surface thereof is a white portion. By controlling the rotational movement of the platen roller 310, the black portion or the white portion can be disposed at a position opposing the image sensor 312 to switch the background color of the original.
In this case, by switching the background color of the original to black, the contour and the like of the original is enhanced. As a result, the outline of the read original can be easily recognized to enable image data consistent with the outline to be created in an easier manner. With a double-sided printed original having largish light transmittance, the background color is preferably switched to black since the printing and the like on a reverse side is enhanced by white background due to the largish light transmittance of the original. Conversely, in the case of an original having print of rather light color and the like and with no printing on a reverse side thereof, it is possible to enhance the printing and the like by switching the background color to white.
The platen roller 310 is driven by a platen roller driving motor 315 such as a stepping motor or the like, and rotates when switching background colors of an original and when cleaning a reading surface of the image sensor 312. When reading an original, the platen roller 310 is controlled so as to stop by a constant holding torque applied by the driving motor 315.
The original 308 having passed the image sensor 312 is conveyed downstream by the conveying roller 303 and subsequently discharged to a discharge tray 309 by a discharge roller 305. The above-described series of original conveying operations is subjected to timing control so as to ensure predetermined original intervals and is continually performed until all of the originals 308 placed on the original mounting table 307 are conveyed. After all of the originals 308 placed on the original mounting table 307 are conveyed, the original mounting table 307 is lowered and returned to its home position. An image reading apparatus that performs the switching of original background colors using a white reference plate and a black board for shading correction instead of a platen roller has been also proposed (refer to Japanese Patent No. 2761736).
A cleaning member 316 that cleans a reading surface of the image sensor 312 is disposed on the platen roller 310. When the platen roller 310 is rotated, the cleaning member 316 passes while contacting the reading surface of the image sensor 312 to clean the reading surface (for example, refer to Japanese Patent No. 3645737).
When consecutively reading originals, cleaning of the reading surface of the image sensor 312 by the cleaning member 316 and a rotational movement of the platen roller 310 to realize a set background color are performed at predetermined timing.
However, with the image reading apparatus described in Japanese Patent No. 3645737, an elastic member protruding from an outer periphery of the platen roller extends in a longitudinal direction of the image sensor which is the main scanning direction in image reading. Therefore, when the platen roller continues to rotate during the conveying of an original, there are cases where the front end of the original catches on the elastic member.
In addition, there may be cases where the elastic member is inadvertently captured in a read image or where variations in density or defocusing occurs due to rippling caused when the elastic member presses a part of the original against a contact glass of the image sensor.
Under such circumstances, conventionally, the contact glass surface of the image sensor is cleaned by, for instance, rotating the platen roller only once immediately after power-on operation or prior to starting image reading of a plurality of originals, or after completion of image reading of a plurality of originals.
However, if contaminants such as paper dust adhere to the contact glass during continuous conveying of a plurality of originals, streaks will occur on the read image read by the image sensor. In addition, if the contaminants remain adhered, streaks will continue to occur even in read images read after the aforementioned original.
With the conventional image reading apparatus described above, when a large number of originals are conveyed, stains adhering to the cleaning member 316 during cleaning of the reading surface of the image sensor 312 becomes deposition. However, after cleaning the reading surface of the image sensor 312, the cleaning member 316 is retreated from the convey path to location inside the apparatus. Therefore, cleaning of deposition of stains adhering on the cleaning member 316 requires disassembling the mechanism around the platen roller 310 and cleaning the cleaning member 316 after removing the platen roller 310 from the apparatus main body, raising a problem in that cleanup work of the cleaning member 316 requires a significant amount of effort.
Furthermore, with the conventional image reading apparatus described above, in the case where a skew of the original 308 occurs, a corner of the original 308 is delayed by the skew, whereby cleaning performed at predetermined timing may cause damages to the original 308 or jamming.
On the other hand, it is conceivable that, the platen roller 310 is rotated to perform cleaning of the reading surface of the image sensor 312 using the cleaning member 316 only when the original has been discharged and conveying of subsequent original has not begun.
However, with such an arrangement the number of read sheets per unit time will be reduced.